Academic Commons Search Resultshttp://academiccommons.columbia.edu/catalog.rss?f%5Bauthor_facet%5D%5B%5D=Kent%2C+Dennis+V.&f%5Bsubject_facet%5D%5B%5D=Paleoclimate+science&q=&rows=500&sort=record_creation_date+desc
Academic Commons Search Resultsen-usA case for a comet impact trigger for the Paleocene/Eocene thermal maximum and carbon isotope excursionhttp://academiccommons.columbia.edu/catalog/ac:180755
Kent, Dennis V.; Cramer, B. S.; Lanci, L.; Wang, D.; Wright, J.D.; Van der Voo, R.http://dx.doi.org/10.7916/D80Z7222Wed, 10 Dec 2014 00:00:00 +0000We hypothesize that the rapid onset of the carbon isotope excursion (CIE) at the Paleocene/Eocene boundary (V55 Ma) may have resulted from the accretion of a significant amount of 12C-enriched carbon from the impact of a V10 km comet, an event that would also trigger greenhouse warming leading to the Paleocene/Eocene thermal maximum and, possibly, thermal dissociation of seafloor methane hydrate. Indirect evidence of an impact is the unusual abundance of magnetic nanoparticles in kaolinite-rich shelf sediments that closely coincide with the onset and nadir of the CIE at three drill sites on the Atlantic Coastal Plain. After considering various alternative mechanisms that could have produced the magnetic nanoparticle assemblage and by analogy with the reported detection of iron-rich nanophase material at the Cretaceous/Tertiary boundary, we suggest that the CIE occurrence was derived from an impact plume condensate. The sudden increase in kaolinite is thus thought to represent the redeposition on the marine shelf of a rapidly weathered impact ejecta dust blanket. Published reports of a small but significant iridium anomaly at or close to the Paleocene/Eocene boundary provide supportive evidence for an impact.Paleoclimate science, Geochemistry, Meteorologydvk2Lamont-Doherty Earth ObservatoryArticlesReply to a comment on ‘‘A case for a comet impact trigger for the Paleocene/Eocene thermal maximum and carbon isotope excursion’’ by G.R. Dickens and J.M. Francishttp://academiccommons.columbia.edu/catalog/ac:180752
Kent, Dennis V.; Cramer, B. S.; Lanci, L.; Wang, D.; Wright, J. D.; Van der Voo, R.http://dx.doi.org/10.7916/D88G8JFTWed, 10 Dec 2014 00:00:00 +0000Contrary to Dickens and Francis’s claim that we ‘challenge the idea of a massive CH4 re- lease during the PETM (Paleocene/Eocene thermal maximum)’, our consideration of an extraterrestrial carbon contribution to the carbon isotope excursion (CIE) is specifically limited to the initial and most rapid decrease in N13C, which accounts for less than half of the full magnitude of the CIE. Thermal dissociation in response to the warm- ing at the PETM is explicitly allowed in our hypothesis, as reiterated in our conclusions that the impact ‘may have triggered a more gradual thermal dissociation of seafloor methane hydrates’. We directly challenge only that portion of the hydrate dissociation hypothesis that relies on gradual warming intrinsic to Earth’s climate system as the triggering mechanism. Such a mechanism is not consistent with the documented essentially synchronous and instantaneous warming and decrease in N13C values at the onset of the event and is also at odds with the occurrence of the CIE during an interval of low amplitude orbital forcing of climate. Instead, we postulate a comet impact as an explanation for the rapid onset of the event.Geochemistry, Paleoclimate sciencedvk2Lamont-Doherty Earth ObservatoryArticlesWhat, if anything, is Quaternary?http://academiccommons.columbia.edu/catalog/ac:180743
Van Couvering, John A.; Berggren, William A.; Aubry, Marie-Pierre; Gradstein, Felix M.; Kent, Dennis V.; Hilgen, Frits J.; Lourens, Lucas J.; McGowran, Brianhttp://dx.doi.org/10.7916/D81Z434JWed, 10 Dec 2014 00:00:00 +0000The formal recognition of Quaternary as a Period/ System was approved by IUGS in June 2009, in accordance with a proposal originated by INQUA. There are reasons to believe that this will have destabilizing consequences for the geological time scale. Until now, the primary divisions of the stratigraphic record, at the Period level and above, have been based on the progressive change of Earth’s biota. The Quaternary, on the other hand, is a paleoclimatic concept based on glacial-interglacial variability, expressed in lithological change. The IUGS vote holds that this paradigm now supersedes the biochronological identity of the Neogene Period/System. Furthermore, to accomodate the most recent INQUA opinion about “when the Ice Ages began”, the ICS agreed to relocate the base of the Pleistocene to 2.59 Ma from 1.81 Ma, enlarging the epoch by 43% and again without regard for its original paleontological definition, or for the vast literature in other fields of Pleistocene research. If history is a guide, the resulting disruption in late Cenozoic marine and vertebrate paleontology, human evolution, paleoceanography and paleoclimatology will be widely resisted, with potential impact on the authority of IUGS. The consequence of abandoning basic principles in order to satisfy the interest of a special group deserves a wider consideration than it has so far received.Paleoclimate science, Geology, Paleontologydvk2Lamont-Doherty Earth ObservatoryAn Exceptional Chronologic, Isotopic, and Clay Mineralogic Record of the Latest Paleocene Thermal Maximum, Bass River, NJ, ODP 174AXhttp://academiccommons.columbia.edu/catalog/ac:176353
Cramer, Benjamin S.; Aubry, Marie-Pierre; Olsson, Richard K.; Miller, Kenneth G.; Wright, James D.; Kent, Dennis V.http://dx.doi.org/10.7916/D8222RZRFri, 08 Aug 2014 00:00:00 +0000A thick, apparently continuous section recording events of the latest Paleocene thermal maximum in a neritic setting was drilled at Bass River State Forest, New Jersey as part of ODP Leg l74AX [Miller, Sugarman, Browning et al., 1998]. Integrated nannofossil and magneto-stratigraphy provides a firm chronology supplemented by planktonic foraminiferal biostratigraphy. This chronologic study indicates that this neritic section rivals the best deep-sea sections in providing a complete record of late Paleocene climatic events. Carbon and oxygen isotopes measured on benthic foraminifera show a major (4.0 %o in carbon, 2.3 %o in oxygen) negative shift correlative with the global latest Paleocene carbon isotope excursion (CIE). A sharp increase in kaolinite content coincides with the isotope shift in the Bass River section, analogous to increases found in several other records. Carbon and oxygen isotopes remain low and kaolinite content remains high for the remainder of the depositional sequence above the CIE (32.5 ft, 9.9 m), which we estimate to represent 300-500 k.y. We interpret these data as indicative of an abrupt shift to a warmer and wetter climate along the North American mid-Atlantic coast, in concert with global events associated with the CIE.Geology, Paleoclimate science, Marine geologydvk2Lamont-Doherty Earth ObservatoryArticlesThe Colorado Plateau Coring Project (CPCP): 100 Million Years of Earth System Historyhttp://academiccommons.columbia.edu/catalog/ac:171429
Olsen, Paul E.; Kent, Dennis V.; Geissman, J.W.; Bachmann, G.; Blakey, R.C.; Gehrels, G.; Irmis, R.B.; Kuerschner, W.; Molina-Garza, R.; Mundil, R.; Sha, J.G.http://dx.doi.org/10.7916/D86Q1V70Thu, 13 Feb 2014 00:00:00 +0000Lasting over 100 million years, the early Mesozoic (252 to 145 Ma) is punctuated by two of the five major mass extinctions of the Phanerozoic (Permo-Triassic and Triassic-Jurassic) plus several smaller extinction events. It witnessed the evolutionary appearance of the modem terrestrial biota including frogs, salamanders, turtles, lizards, crocodilians, dinosaurs, birds, and mammals, and spans a time of dramatic climate changes on the continents. What is arguably the richest record of these events lies in the vast (- 2.5 million km2) complex of epicontinental basins in the western part of Pangea, now largely preserved on the Colorado Plateau (Fig.l). Since the mid-19th century, classic studies of these basins, their strata, and their fossils have made this succession instrumental in framing our context of the early Mesozoic Earth system as reflected in the international literature. Despite this long and distinguished history of study of the Colorado Plateau region, striking ambiguities in temporal resolution, major uncertainties in global correlations, and significant doubts about paleolatitudinal position hamper incorporation of the huge amount of information from the region into-tests of major competing climatic, biotic, and tectonic hypotheses and a fundamental understanding of Earth system processes.Geology, Geomorphology, Paleoclimate science, Paleontologypeo1, dvk2Lamont-Doherty Earth ObservatoryArticlesResponse to Comment on “Atmospheric PCo2 Perturbations Associated with the Central Atlantic Magmatic Province”http://academiccommons.columbia.edu/catalog/ac:171432
Schaller, Morgan F.; Wright, James D.; Kent, Dennis V.http://dx.doi.org/10.7916/D8SJ1HKWThu, 13 Feb 2014 00:00:00 +0000Rampino and Caldeira argue that the first pulse of the Central Atlantic Magmatic Province would increase the concentration of atmospheric carbon dioxide (PCO2) by only 400 parts per million if erupted over 20,000 years, whereas we observed a doubling within this interval. In the absence of any data to the contrary, we suggest that a more rapid (≤1000-year) eruption is sufficient to explain this observation without relying on thermogenic degassing.Atmospheric chemistry, Paleoclimate sciencedvk2Lamont-Doherty Earth ObservatoryArticlesA critique of evidence for human occupation of Europe older than the Jaramillo subchron (∼1 Ma): Comment on Toro-Moyano et al. (2013)http://academiccommons.columbia.edu/catalog/ac:171426
Muttoni, Giovanni; Scardia, Giancarlo; Kent, Dennis V.http://dx.doi.org/10.7916/D8TM784FWed, 12 Feb 2014 00:00:00 +0000The recently dated human tooth from Barranco León, Spain, would seem to indicate that hominins were present in southern Europe as early asw1.4 Ma (millions of years ago) based on electron spin resonance (ESR) ages on quartz grains coupled with magnetostratigraphic and biochronologic correlations (Toro-Moyano et al., 2013). We suggest that the evidence for human occupation of Europe prior to 1 Ma is highly equivocal.Paleoclimate science, Geophysicsdvk2Lamont-Doherty Earth ObservatoryArticlesEvidence for abundant isolated magnetic nanoparticles at the Paleocene–Eocene boundaryhttp://academiccommons.columbia.edu/catalog/ac:157513
Wang, Huapei; Kent, Dennis V.; Jackson, Michael J.http://hdl.handle.net/10022/AC:P:19325Mon, 11 Mar 2013 00:00:00 +0000New rock magnetic results (thermal fluctuation tomography, high-resolution first-order reversal curves and low temperature measurements) for samples from the Paleocene–Eocene thermal maximum and carbon isotope excursion in cored sections at Ancora and Wilson Lake on the Atlantic Coastal Plain of New Jersey indicate the presence of predominantly isolated, near-equidimensional single-domain magnetic particles rather than the chain patterns observed in a cultured magnetotactic bacteria sample or magnetofossils in extracts. The various published results can be reconciled with the recognition that chain magnetosomes tend to be preferentially extracted in the magnetic separation process but, as we show, may represent only a small fraction of the overall magnetic assemblage that accounts for the greatly enhanced magnetization of the carbon isotope excursion sediment but whose origin is thus unclear.Paleoclimate science, Geologydvk2Lamont-Doherty Earth ObservatoryArticlesModulation of Late Cretaceous and Cenozoic climate by variable drawdown of atmospheric pCO2 from weathering of basaltic provinces on continents drifting through the equatorial humid belthttp://academiccommons.columbia.edu/catalog/ac:157502
Kent, Dennis V.; Muttoni, G.http://hdl.handle.net/10022/AC:P:19319Mon, 11 Mar 2013 00:00:00 +0000The small reservoir of carbon dioxide in the atmosphere (pCO2) that modulates climate through the greenhouse effect reflects a delicate balance between large fluxes of sources and sinks. The major long-term source of CO2 is global outgassing from sea-floor spreading, subduction, hotspot activity, and metamorphism; the ultimate sink is through weathering of continental silicates and deposition of carbonates. Most carbon cycle models are driven by changes in the source flux scaled to variable rates of ocean floor production, but ocean floor production may not be distinguishable from being steady since 180 Ma. We evaluate potential changes in sources and sinks of CO2 for the past 120 Ma in a paleogeographic context. Our new calculations show that decarbonation of pelagic sediments by Tethyan subduction contributed only modestly to generally high pCO2 levels from the Late Cretaceous until the early Eocene, and thus shutdown of this CO2 source with the collision of India and Asia at the early Eocene climate optimum at around 50 Ma was inadequate to account for the large and prolonged decrease in pCO2 that eventually allowed the growth of significant Antarctic ice sheets by around 34 Ma. Instead, variation in area of continental basalt terranes in the equatorial humid belt (5° S–5° N) seems to be a dominant factor controlling how much CO2 is retained in the atmosphere via the silicate weathering feedback. The arrival of the highly weatherable Deccan Traps in the equatorial humid belt at around 50 Ma was decisive in initiating the long-term slide to lower atmospheric pCO2, which was pushed further down by the emplacement of the 30 Ma Ethiopian Traps near the equator and the southerly tectonic extrusion of SE Asia, an arc terrane that presently is estimated to account for 1/4 of CO2 consumption from all basaltic provinces that account for ~1/3 of the total CO2 consumption by continental silicate weathering (Dessert et al., 2003). A negative climate-feedback mechanism that (usually) inhibits the complete collapse of atmospheric pCO2 is the accelerating formation of thick cation-deficient soils that retard chemical weathering of the underlying bedrock. Nevertheless, equatorial climate seems to be relatively insensitive to pCO2 greenhouse forcing and thus with availability of some rejuvenating relief as in arc terranes or thick basaltic provinces, silicate weathering in this venue is not subject to a strong negative feedback, providing an avenue for ice ages. The safety valve that prevents excessive atmospheric pCO2 levels is the triggering of silicate weathering of continental areas and basaltic provinces in the temperate humid belt. Excess organic carbon burial seems to have played a negligible role in atmospheric pCO2 over the Late Cretaceous and Cenozoic.Paleoclimate science, Atmospheric chemistrydvk2Lamont-Doherty Earth ObservatoryArticlesRapid emplacement of the Central Atlantic Magmatic Province as a net sink for CO2http://academiccommons.columbia.edu/catalog/ac:156069
Schaller, Morgan; Wright, James; Kent, Dennis V.; Olsen, Paul E.http://hdl.handle.net/10022/AC:P:18859Wed, 30 Jan 2013 00:00:00 +0000Recent evidence from the ~201.5 Ma Central Atlantic Magmatic Province (CAMP) in the Newark rift basin demonstrates that this Large Igneous Province produced a transient doubling of atmospheric pCO2, followed by a falloff to pre-eruptive concentrations over ~300 kyr. This paper confirms the short-term findings from the Newark basin, and tests the million-year effects of the CAMP volcanism on Early Jurassic pCO2 from strata in the corollary Hartford basin of Eastern North America (ENA) also using the pedogenic carbonate paleobarometer. We !nd pCO2 levels for pre-CAMP background of 2000±700 ppm (at S(z)=3000±1000 ppm), increasing to ~5000±1700 ppm immediately above the first lava "ow unit, consistent with observations from the Newark. The longer post-extrusive Portland Formation of the Hartford basin records a fourth pulse of pCO2 to ~4500±1200 ppm, about 240 kyr after the last lava recorded in the ENA section. We interpret this fourth increase as due to a major episode of volcanism, and revise the main CAMP duration to 840±60 kyr. The Portland also records a post-eruptive decrease inpCO2 reaching pre-eruptive background concentrations of ~2000 ppm in only ~300 kyr, and continuing to levels below pre-CAMP background over the subsequent 1.5Myr following the final episode of eruptions. Geochemical modeling (using modified COPSE code) demonstrates that the rapidity of the pCO2 decreases, and fall to concentrations below background can be accounted for by a 1.5-fold amplification of the continental silicate weathering response due to the presence of the CAMP basalts themselves. These results demonstrate that a continental "flood basalt capable of producing a short-term perturbation of the carbon system may actually have an overall netcooling effect on global climates due to a long-term net-decrease in pCO2 to below pre-eruptive levels, as previous models have suggested followed the emplacement of the Deccan Traps.Paleoclimate science, Paleontologydvk2, peo1Lamont-Doherty Earth ObservatoryArticlesRapid emplacement of the Central Atlantic Magmatic Province as a net sink for CO2http://academiccommons.columbia.edu/catalog/ac:145601
Schaller, Morgan F.; Wright, James D.; Kent, Dennis V.; Olsen, Paul E.http://hdl.handle.net/10022/AC:P:12897Wed, 28 Mar 2012 00:00:00 +0000Recent evidence from the ~ 201.5 Ma Central Atlantic Magmatic Province (CAMP) in the Newark rift basin demonstrates that this Large Igneous Province produced a transient doubling of atmospheric pCO2, followed by a falloff to pre-eruptive concentrations over ~ 300 kyr. This paper confirms the short-term findings from the Newark basin, and tests the million-year effects of the CAMP volcanism on Early Jurassic pCO2 from strata in the corollary Hartford basin of Eastern North America (ENA) also using the pedogenic carbonate paleobarometer. We find pCO2 levels for pre-CAMP background of 2000 ± 700 ppm (at S(z) = 3000 ± 1000 ppm), increasing to ~ 5000 ± 1700 ppm immediately above the first lava flow unit, consistent with observations from the Newark. The longer post-extrusive Portland Formation of the Hartford basin records a fourth pulse of pCO2 to ~ 4500 ± 1200 ppm, about 240 kyr after the last lava recorded in the ENA section. We interpret this fourth increase as due to a major episode of volcanism, and revise the main CAMP duration to 840 ± 60 kyr. The Portland also records a post-eruptive decrease in pCO2 reaching pre-eruptive background concentrations of ~ 2000 ppm in only ~ 300 kyr, and continuing to levels below pre-CAMP background over the subsequent 1.5 Myr following the final episode of eruptions. Geochemical modeling (using modified COPSE code) demonstrates that the rapidity of the pCO2 decreases, and fall to concentrations below background can be accounted for by a 1.5-fold amplification of the continental silicate weathering response due to the presence of the CAMP basalts themselves. These results demonstrate that a continental flood basalt capable of producing a short-term perturbation of the carbon system may actually have an overall net-cooling effect on global climates due to a long-term net-decrease in pCO2 to below pre-eruptive levels, as previous models have suggested followed the emplacement of the Deccan Traps.Paleoclimate sciencedvk2, peo1Lamont-Doherty Earth Observatory, Earth and Environmental SciencesArticlesHigh-resolution early Mesozoic Pangean climatic transect in lacustrine environmentshttp://academiccommons.columbia.edu/catalog/ac:144004
Olsen, Paul E.; Kent, Dennis V.http://hdl.handle.net/10022/AC:P:12402Mon, 30 Jan 2012 00:00:00 +0000Analysis of 6700 m of core from the Newark rift basin in New Jersey, USA provides a high-resolution astronomically calibrated magnetic polarity time scale for the Late Triassic and Early Jurassic spanning about 33 million years. This time scale, and its application elsewhere, allows a significant simplification of the pattern of climate-sensitive facies in the early Mesozoic basins of the central and north Atlantic margins. Coals and deep-water lacustrine deposits were produced at the paleoequator (Richmond-type sequences), while strikingly cyclical lacustrine and playa deposits were produced \00 to the north and south (Newark-type lacustrine sequences). At 10-30 ON, eolian dunes, playas sediments and evaporites were deposited (Fundy-type sequences). Farther north, shallow-water lacustrine red beds were deposited (Fleming Fjord-type sequences), while yet farther north (-40°), perennial-lake black mudstones and coals again dominated in the humid temperate zone (Kap Stewart-type sequences). Central Pangea drifted north about 10° during the Late Triassic, and the vertical sequence of climate-sensitive facies in individual basins changed as the basins passed through different climate zones. This simple zonal climate pattern explains most first-order changes in overall lacustrine sequences seen in the rift zone. Lakelevel cycles of Milankovitch origin change in a predicable way with the latitudinal shifts in climate and lacustrine style. Roughly \0 ky precessional cycles dominate within a few degrees of the equator, while -20 ky precessional cycles are dominant northward to about 30 ON where 40 ky obliquity cycles become evident in lake-level records.Geology, Paleoclimate sciencepeo1, dvk2Lamont-Doherty Earth Observatory, Earth and Environmental SciencesArticlesPaleogene time scale miscalibration: Evidence from the dating of the North Atlantic igneous provincehttp://academiccommons.columbia.edu/catalog/ac:143804
Aubry, Marie-Pierre; Swisher, Carl C.; Kent, Dennis V.; Berggren, William A.http://hdl.handle.net/10022/AC:P:12328Mon, 23 Jan 2012 00:00:00 +0000Jolley et al. (2002) have proposed that the date of the Paleocene - Eocene thermal maximum is ca. 60 Ma, at least 5 m.y. older than currently estimated and, as a result, argue that the Paleogene time scale of Berggren et al. (1995) is grossly miscalibrated. The implications of this proposal are implausible, and we attribute the discrepancy in age noted by Jolley et al. (2002) to miscorrelation of the Staffa-type palynofloras and ambiguous isotopic dates from the North Atlantic igneous province.Geology, Paleoclimate sciencedvk2Lamont-Doherty Earth ObservatoryArticlesApparent correlation of palaeomagnetic intensity and climatic records in deep-sea sedimentshttp://academiccommons.columbia.edu/catalog/ac:143634
Kent, Dennis V.http://hdl.handle.net/10022/AC:P:12285Fri, 20 Jan 2012 00:00:00 +0000Most reports of a correlation between Pleistocene climate and geomagnetic field intensity rely strongly on the assumption that sediment natural remanent magnetic (NRM) intensity provides a record of geomagnetic field strength and is not sensitive to local changes in properties of the sediment. Critical assessment of relevant data presented here and elsewhere from deep-sea sediment cores shows that a pronounced dependence of NRM intensity on sediment composition can occur which implies that this assumption is unlikely to be generally valid. As sediment composition often reflects varying depositional conditions induced by climatic change, the significance of correlations proposed between Pleistocene palaeomagnetism and climatic indicators in deep-sea sediments may be less dramatic than sometimes supposed.Paleoclimate sciencedvk2Lamont-Doherty Earth ObservatoryArticlesGeomagnetic excursions and climate change: Reply to Comment by M. R. Rampinohttp://academiccommons.columbia.edu/catalog/ac:143631
Kent, Dennis V.http://hdl.handle.net/10022/AC:P:12283Fri, 20 Jan 2012 00:00:00 +0000Rampino is correct in stating that, unlike NRM intensity fluctuations observed in some cores, anomalous NRM directions interpreted as geomagnetic excursions are not readily explained by changes in lithology and magnetic mineral content. The question of excursions, particularly their temporal and spatial distribution, can be argued at length (see, for example, ref. 2). Here I will simply illustrate some of the associated problems by considering the record of purported excursions in a single critical core, V20-108, which provides an important basis for several contributions seeking a link between geomagnetism and climate.Paleoclimate sciencedvk2Lamont-Doherty Earth ObservatoryArticlesEquatorial convergence of India and early Cenozoic climate trendshttp://academiccommons.columbia.edu/catalog/ac:143488
Kent, Dennis V.; Muttoni, Giovannihttp://hdl.handle.net/10022/AC:P:12260Thu, 19 Jan 2012 00:00:00 +0000India's northward flight and collision with Asia was a major driver of global tectonics in the Cenozoic and, we argue, of atmospheric CO2 concentration (pCO2) and thus global climate. Subduction of Tethyan oceanic crust with a carpet of carbonate-rich pelagic sediments deposited during transit beneath the high-productivity equatorial belt resulted in a component flux of CO2 delivery to the atmosphere capable to maintain high pCO2 levels and warm climate conditions until the decarbonation factory shut down with the collision of Greater India with Asia at the Early Eocene climatic optimum at ≈50 Ma. At about this time, the India continent and the highly weatherable Deccan Traps drifted into the equatorial humid belt where uptake of CO2 by efficient silicate weathering further perturbed the delicate equilibrium between CO2 input to and removal from the atmosphere toward progressively lower pCO2 levels, thus marking the onset of a cooling trend over the Middle and Late Eocene that some suggest triggered the rapid expansion of Antarctic ice sheets at around the Eocene-Oligocene boundary.Geomorphology, Paleoclimate sciencedvk2Lamont-Doherty Earth ObservatoryArticlesClimatically driven biogeographic provinces of Late Triassic tropical Pangeahttp://academiccommons.columbia.edu/catalog/ac:143494
Whiteside, Jessica H.; Grogan, Danielle S.; Olsen, Paul E.; Kent, Dennis V.http://hdl.handle.net/10022/AC:P:12262Thu, 19 Jan 2012 00:00:00 +0000Although continents were coalesced into the single landmass Pangea, Late Triassic terrestrial tetrapod assemblages are surprisingly provincial. In eastern North America, we show that assemblages dominated by traversodont cynodonts are restricted to a humid 6° equatorial swath that persisted for over 20 million years characterized by "semiprecessional" (approximately 10,000-y) climatic fluctuations reflected in stable carbon isotopes and sedimentary facies in lacustrine strata. More arid regions from 5-20°N preserve procolophonid-dominated faunal assemblages associated with a much stronger expression of approximately 20,000-y climatic cycles. In the absence of geographic barriers, we hypothesize that these variations in the climatic expression of astronomical forcing produced latitudinal climatic zones that sorted terrestrial vertebrate taxa, perhaps by excretory physiology, into distinct biogeographic provinces tracking latitude, not geographic position, as the proto-North American plate translated northward. Although the early Mesozoic is usually assumed to be characterized by globally distributed land animal communities due to of a lack of geographic barriers, strong provinciality was actually the norm, and nearly global communities were present only after times of massive ecological disruptions.Paleoclimate sciencepeo1, dvk2Lamont-Doherty Earth Observatory, Earth and Environmental SciencesArticlesOrbital tuning of geomagnetic polarity time-scaleshttp://academiccommons.columbia.edu/catalog/ac:143516
Kent, Dennis V.http://hdl.handle.net/10022/AC:P:12268Thu, 19 Jan 2012 00:00:00 +0000Milankovitch climate cyclicity and magnetic polarity stratigraphy are being successfully combined as a powerful geochronometer in the astronomical polarity time-scale (APTS). The APTS for 0 to 5.23 Ma has been rapidly accepted as the definitive chronology for the Pliocene and Pleistocene against which even high precision radiometric dating is now calibrated. Extensions of astronomical calibration to the late Miocene (5.23 Ma to ca.10 Ma) in Mediterranean and Pacific marine sections may show mutual disagreements on the order of a 100 ka eccentricity cycle, which amounts to an uncertainty of only ca.1% the age. Orbital eccentricity periods are thought to remain stable over very long times and thus provide the possibility of precise relative age control in the pre-Neogene. An APTS, for example, has been developed in a thick lacustrine section of Late Triassic age (ca.202 to 233 Ma) on the basis of the 404 ka orbital eccentricity cycle modulating the expression of the precession climate cyclicity. Finally, there has been renewed speculation about an obliquity-modulated precessional geodynamo based on periodicities in relative palaeointensity data from Ocean Drilling Program sediment cores.Paleoclimate sciencedvk2Lamont-Doherty Earth ObservatoryArticlesLong-period Milankovitch cycles from the Late Triassic and Early Jurassic of eastern North America . . .http://academiccommons.columbia.edu/catalog/ac:143512
Olsen, Paul E.; Kent, Dennis V.http://hdl.handle.net/10022/AC:P:12267Thu, 19 Jan 2012 00:00:00 +0000During the Late Triassic and Early Jurassic the Newark rift basin of the northeastern US accumulated in excess 5 km of continental, mostly lacustrine strata that show a profound cyclicity previously interpreted as caused by the astronomical forcing of tropical climate. The Newark record is known virtually in its entirety as a result of scientific and other coring and provides what is arguably one of the longest records of climate cyclicity available. Two proxies of water depth and hence climate in this record are a classification of sedimentary structures (depth ranks) and sediment colour. The depth rank and colour depth series display a full range of climatic precession related cycles. Here, we tune the depth rank and colour records to the 404 ka astronomical cycle and use this tuned record to explore the existence and origin of very longâ€“period climate. We find highly significant periods of climatic precession modulation at periods of ca.1.75 Ma, 1 Ma and 700 ka in not only the depth rank and colour records, but also in the sedimentation rate curve derived from the tuning process. We then use the colour and depth rank timeâ€“series to construct an astronomically tuned timeâ€“scale for the Late Triassic. While the Newark higherâ€“frequency eccentricity cycles that modulate precession are indistinguishable from today, the 1.75 Ma cycle is significantly different from predictions based on the present day fundamental frequencies of the planets (i.e. 2.5 Ma) and provides the first geological evidence of the chaotic behaviour of the inner planets, otherwise known only from numerical calculations.Paleoclimate sciencepeo1, dvk2Lamont-Doherty Earth Observatory, Earth and Environmental SciencesArticlesSynchrony between the Central Atlantic magmatic province and the Triassic-Jurassic mass-extinction event?http://academiccommons.columbia.edu/catalog/ac:143354
Whiteside, Jessica H.; Olsen, Paul E.; Kent, Dennis V.; Fowell, Sarah J.; Et-Touhami, Mohammedhttp://hdl.handle.net/10022/AC:P:12223Tue, 17 Jan 2012 00:00:00 +0000We present new data and a synthesis of cyclostratigraphic, lithostratigraphic, biostratigraphic, and published magnetostratigraphic and basalt geochemical data from eastern North America and Morocco in an attempt to clarify the temporal relationship between the Triassic–Jurassic mass extinction (∼ 202 Ma) and Earth's largest sequence of continental flood basalts, the Central Atlantic magmatic province (CAMP). Newly discovered zones of reverse polarity within CAMP flow sequences of Morocco have been hypothesized by Marzoli et al. [Marzoli, A., Bertrand, H., Knight, K.B., Cirilli, S., Buratti, N., Vérati, C., Nomade, S., Renne, P.R., Youbi, N., Martini, R., Allenbach, K., Neuwerth, R., Rapaille, C., Zaninetti, L., Bellieni, G., 2004. Synchrony of the Central Atlantic magmatic province and the Triassic–Jurassic boundary climatic and biotic crisis. Geology 32, 973–976.] and Knight et al. [Knight, K.B., Nomade, S., Renne, P.R., Marzoli, A., Betrand, H., Youbi, N., 2004. The Central Atlantic Magmatic Province at the Triassic–Jurassic boundary: paleomagnetic and 40Ar/30Ar evidence from Morocco for brief, episodic volcanism. Earth and Planetary Science Letters 228, 143–160.] as correlates of a very short, uppermost Triassic age reverse chron in the Newark basin, thus suggesting that much of the Moroccan CAMP was synchronous with or predates the Triassic–Jurassic boundary. Here, however, we explain these apparent reverse polarity zones as possible correlatives of poorly sampled lower Jurassic basalt flow sequences and overlying strata in eastern North America and lower Jurassic reverse polarity sequences recognized by others in the Paris basin. A revised Milankovitch cyclostratigraphy based on new core and field data constrains the duration of eastern North America basaltic flows to ∼ 610 ky after the Triassic–Jurassic palynological turnover event. Palynological data indicates correlation of the initial carbon isotopic excursion of Hesselbo et al. [Hesselbo, S.P., Robinson, S.A., Surlyk, F., Piasecki, S., 2002. Terrestrial and marine extinction at the Triassic–Jurassic boundary synchronized with major carbon-cycle perturbation: a link to initiation of massive volcanism. Geology 30, 251–254.] at St. Audrie's Bay to the palynological turnover event and vertebrate extinction level in eastern North America, suggesting a revised magnetostratigraphic correlation and robust carbon isotopic tests of the Marzoli–Knight hypothesis. We conclude that as yet there are no compelling data showing that any of the CAMP predated or was synchronous with the Triassic–Jurassic extinction event.Paleoclimate sciencepeo1, dvk2Lamont-Doherty Earth Observatory, Earth and Environmental SciencesArticlesSynchrony between the Central Atlantic magmatic province and the Triassicâ€“Jurassic mass-extinction event? Reply to Marzoli et al.http://academiccommons.columbia.edu/catalog/ac:143357
Whiteside, Jessica H.; Olsen, Paul E.; Kent, Dennis V.; Fowell, Sarah J.; Et-Touhami, Mohammedhttp://hdl.handle.net/10022/AC:P:12224Tue, 17 Jan 2012 00:00:00 +0000We are very pleased with the attention, long overdue, that the Triassic–Jurassic boundary and associated events, such as the CAMP, are receiving. This can only lead to greater specificity of hypotheses and greater understanding in the long run, and it is worth emphasizing some broad areas of agreement. Marzoli et al. (2008-this volume) points out the closeness in time of CAMP and Tr–J extinctions, and on this we all agree. We also agree that the systematic differences among different isotopic systems used for dating is a challenge to determining the relative timing of events dated with different techniques. This problem, however, seem to be fading as high-precision single-crystal U–Pb dates (206Pb/238U) are available from a variety of tuffs interbedded with marine strata as well as the North Mountain Basalt of Nova Scotia, which lies above the palynological Triassic–Jurassic extinction event in Nova Scotia. Schoene et al. (2006) obtained an age of 201.27 ± 0.03 Ma from this basalt, which is very close to an age of 201.5 Ma for a tuff 1 m above the last local occurrence of the topmost Triassic guide-fossil, the ammonite Choristoceras in a marine section in Peru (Schaltegger et al., 2007), presumably very close to the Triassic–Jurassic extinction event. Schaltegger et al. (2007) also obtained an age of 199.5 Ma for the Hettangian–Sinemurian boundary from the latter section. Consistent with these ages, Pálfy and Mundil (2006) obtained ages of 200.6 ± 0.3 Ma for an ash layer in ammonite-bearing Middle Hettangian marine sediments in, Alaska, and 198.0 ± 0.6 Ma for a tuff layer in Early Sinemurian sediments in Hungary. These dates are not compatible with the multi-crystal age for the Triassic–Jurassic boundary of 199.6 ± 0.3 Ma of Pálfy and Mundil (2006), a fact recognized by Pálfy and Mundil (2006). Thus, we are in complete agreement that the Triassic–Jurassic extinction event is extremely close in time to the onset of the CAMP. The question is, "are any of the known flows of the CAMP actually at or before this extinction event?". That is the key issue dealt with by Whiteside et al. (2007), and it is a possibility that we recognize as completely plausible, but not yet demonstrated. It is in that spirit of general agreement that we reply to Marzoli et al.'s, comment. We note, however, that their comment touches on far too many points to adequately address in this reply, and we chose to focus our response on their most substantive issues, recalling that our paper was focusing on the testable aspects of their overall hypothesis. We deal with their criticisms in the order they present them.Paleoclimate sciencepeo1, dvk2Lamont-Doherty Earth Observatory, Earth and Environmental SciencesArticlesHuman migration into Europe during the late Early Pleistocene climate transitionhttp://academiccommons.columbia.edu/catalog/ac:143363
Muttoni, Giovanni; Scardia, Giancarlo; Kent, Dennis V.http://hdl.handle.net/10022/AC:P:12226Tue, 17 Jan 2012 00:00:00 +0000A critical assesment of the available magnetostratigraphic and/or radiometric age constraints on key sites bearing hominin remains and/or lithic industries from southern Europe (Italy, France, Spain) leads us to propose that the main window of early hominin presence in southern Europe is broadly comprised between the Jaramillo subchron and the Brunhes–Matuyama boundary (i.e., subchron C1r.1r, 0.99–0.78 Ma). Within the dating uncertainties, this ~ 200 ky time window broadly coincides with the late Early Pleistocene global climate transition that contains marine isotope stage (MIS) 22 (~ 0.87 Ma), the first prominent cold stage of the Pleistocene. We suggest that aridification in North Africa and Eastern Europe, particularly harsh during MIS 22 times, triggered migration pulses of large herbivores, particularly elephants, from these regions into southern European refugia, and that hominins migrated with them. Finally, we speculate on common pathways of late Early Pleistocene dispersal of elephants and hominins from their home in savannah Africa to southern Europe, elephant and hominin buen retiro. In particular, we stress the importance of the Po Valley of northern Italy that became largely and permanently exposed only since MIS 22, thus allowing possibly for the first time in the Pleistocene viable new migration routes for large mammals and hominins across northern Italy to southern France and Spain in the west.Paleoclimate sciencedvk2Lamont-Doherty Earth ObservatoryArticlesBolide summer: The Paleocene/Eocene thermal maximum as a response to an extraterrestrial triggerhttp://academiccommons.columbia.edu/catalog/ac:143345
Cramer, Benjamin S.; Kent, Dennis V.http://hdl.handle.net/10022/AC:P:12216Tue, 17 Jan 2012 00:00:00 +0000The standard paradigm that the Paleocene/Eocene thermal maximum (PETM) represents a threshold event intrinsic to Earth's climate and connected in some way with long-term warming has influenced interpretations of the geochemical, climate, and biological perturbations that occurred at this event. As recent high-resolution data have demonstrated that the onset of the event was geologically instantaneous, attempts to account for the event solely through endogenous mechanisms have become increasingly strained. The rapid onset of the event indicates that it was triggered by a catastrophic event which we suggest was most likely a bolide impact. We discuss features of the PETM that require explanation and argue that mechanisms that have previously been proposed either cannot explain all of these features or would require some sort of high-energy trigger. A bolide impact could provide such a trigger and, in the event of a comet impact, could contribute directly to the shape of the carbon isotope curve. We introduce a carbon cycle model that would explain the PETM by global warming following a bolide impact, leading to the oxidation of terrestrial organic carbon stores built up during the late Paleocene. Our intention is to encourage other researchers to seriously consider an impact trigger for the PETM, especially in the absence of plausible alternative mechanisms.Paleoclimate sciencedvk2Lamont-Doherty Earth ObservatoryArticlesWidespread formation of cherts during the early Eocene climate optimumhttp://academiccommons.columbia.edu/catalog/ac:143348
Muttoni, Giovanni; Kent, Dennis V.http://hdl.handle.net/10022/AC:P:12221Tue, 17 Jan 2012 00:00:00 +0000Radiolarian cherts in the Tethyan realm of Jurassic age were recently interpreted as resulting from high biosiliceous productivity along upwelling zones in subequatorial paleolatitudes the locations of which were confirmed by revised paleomagnetic estimates. However, the widespread occurrence of cherts in the Eocene suggests that cherts may not always be reliable proxies of latitude and upwelling zones. In a new survey of the global spatio-temporal distribution of Cenozoic cherts in Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) sediment cores, we found that cherts occur most frequently in the Paleocene and early Eocene, with a peak in occurrences at ~50 Ma that is coincident with the time of highest bottom water temperatures of the early Eocene climatic optimum (EECO) when the global ocean was presumably characterized by reduced upwelling efficiency and biosiliceous productivity. Cherts occur less commonly during the subsequent Eocene global cooling trend. Primary paleoclimatic factors rather than secondary diagenetic processes seem therefore to control chert formation. This timing of peak Eocene chert occurrence, which is supported by detailed stratigraphic correlations, contradicts currently accepted models that involve an initial loading of large amounts of dissolved silica from enhanced weathering and/or volcanism in a supposedly sluggish ocean of the EECO, followed during the subsequent middle Eocene global cooling by more vigorous oceanic circulation and consequent upwelling that made this silica reservoir available for enhanced biosilicification, with the formation of chert as a result of biosilica transformation during diagenesis. Instead, we suggest that basin-basin fractionation by deep-sea circulation could have raised the concentration of EECO dissolved silica especially in the North Atlantic, where an alternative mode of silica burial involving widespread direct precipitation and/or absorption of silica by clay minerals could have been operative in order to maintain balance between silica input and output during the upwelling-deficient conditions of the EECO. Cherts may therefore not always be proxies of biosiliceous productivity associated with latitudinally focused upwelling zones.Paleoclimate sciencedvk2Lamont-Doherty Earth ObservatoryArticlesEnd-Triassic calcification crisis and blooms of organic-walled 'disaster species'http://academiccommons.columbia.edu/catalog/ac:143351
Schootbrugge, B. van de; Tremolada, F.; Rosenthal, Y.; Bailey, T. R.; Feist-Burkhardt, S.; Brinkhuis, H.; Pross, J.; Kent, Dennis V.; Falkowski, P. G.http://hdl.handle.net/10022/AC:P:12222Tue, 17 Jan 2012 00:00:00 +0000The Triassic–Jurassic (T–J) mass-extinction event is marked by isotope anomalies in organic (δ13Corg) and carbonate carbon (δ13Ccarb) reservoirs. These have been attributed to a (rapid) 4-fold rise in pCO2 as a result of massive flood basalt volcanism and/or methane hydrate dissociation. Here we examine the response of marine photosynthetic phytoplankton to the proposed perturbation in the carbon cycle. Our high-resolution micropalaeontological analysis of T–J boundary beds at St Audrie's Bay in Somerset, UK, provides evidence for a bio-calcification crisis that is characterized by (1) extinction and malformation in calcareous nannoplankton and (2) contemporaneous blooms of organic-walled, green algal 'disaster' species which comprise in one case > 70% of the total palynomorph fraction. Blooms of prasinophytes and acritarchs occur at the onset and in association with a prominent negative shift in δ13Corg values close to the first appearance of the Early Jurassic ammonite Psiloceras planorbis. Across the same interval we obtained palaeotemperature and palaeosalinity estimates from oyster low-Mg calcite based on Mg/Ca, Sr/Ca and δ18O records. The results of our palynological and geochemical analyses strongly suggest that shallow marine basins in NW Europe during this period became salinity stratified, inducing anoxic conditions. The T–J boundary event shows similarities with the Permian–Triassic (P–T) mass-extinction event, which was also marked by extensive flood basalt volcanism, negative excursions in carbon isotope records, a bio-calcification crisis, the development of shallow-marine anoxia and mass abundances of acritarchs in the Early Triassic. This leads us to suggest that the proliferation of green algal phytoplankton may be symptomatic of elevated carbon dioxide levels in the atmosphere and oceans during mass-extinction events.Paleoclimate sciencedvk2Lamont-Doherty Earth ObservatoryArticlesRhaetian magneto-biostratigraphy from the Southern Alps (Italy): Constraints on Triassic chronologyhttp://academiccommons.columbia.edu/catalog/ac:143360
Muttoni, Giovanni; Kent, Dennis V.; Jadoul, Flavio; Olsen, Paul E.; Rigo, Manuel; Galli, Maria Teresa; Nicora, Aldahttp://hdl.handle.net/10022/AC:P:12225Tue, 17 Jan 2012 00:00:00 +0000New Late Triassic–earliest Jurassic magneto-biostratigraphic data have been obtained from three overlapping sections in the Southern Alps, Italy (Costa Imagna, Brumano, Italcementi Quarry), composed of ~ 520 m of shallow-marine carbonates outcropping in stratigraphic continuity. Characteristic magnetic components of presumed depositional age record a sequence of 9 normal and reverse polarity magnetozones (as defined by at least three stratigraphically superposed samples) linked by conodont and palynofloral evidence from this study and the literature to Rhaetian to Triassic–Jurassic boundary age. This represents a significantly larger number of polarity zones than previously recognized in more condensed Rhaetian sections from the literature, and by inference represents more time. These data are placed in a broader Late Triassic temporal framework by means of correlations to published magneto-biostratigraphic data from the Tethyan marine Pizzo Mondello section and the Newark astronomical polarity time scale (APTS). This framework is consistent with a position of the Norian–Rhaetian boundary (as defined at Brumano and Pizzo Mondello by the first appearance of Misikella posthernsteini) within Newark magnetozones E17r–E19r in the ~ 207–210 Ma time interval, in basic agreement with the position originally estimated in the Newark using pollen biostratigraphy (E18 at 208–209 Ma). This framework is also consistent with the position of the Triassic–Jurassic boundary interval (placed at Italcementi Quarry at the acme of Kraeuselisporites reissingeri coincident with a negative carbon isotope excursion) correlative to just above Newark magnetozone E23r and just below the oldest CAMP lavas dated at ~ 202 Ma. Hence, we estimate the duration of the Rhaetian to be ~ 5.5–8.5 Myr (or even longer if the Triassic–Jurassic boundary is instead placed above the negative carbon isotope excursion as at Kuhjoch, which is the designated GSSP for the base of the Hettangian), and encompassing 9 magnetozones. This duration contrasts with a duration of ~ 2 Myr and only ~ 4 magnetozones in several alternative published magneto-biostratigraphic schemes.Paleoclimate sciencedvk2, peo1Lamont-Doherty Earth Observatory, Earth and Environmental SciencesArticlesEmergence of Venice during the Pleistocenehttp://academiccommons.columbia.edu/catalog/ac:143384
Kent, Dennis V.; Rio, Domenico; Massari, Francesco; Kukla, George; Lanci, Lucahttp://hdl.handle.net/10022/AC:P:12233Tue, 17 Jan 2012 00:00:00 +0000The Pleistocene history of sea-level change for the Venice region was reconstructed using an integrated magneto-bio-cyclo-stratigraphy of lithofacies and a published palynofloral analysis of continuously cored sediments in a 950-meter-deep drill core. The basin in which the Venice region is located collapsed at ∼1.8 Ma with slow sediment accumulation in the deeper-water starved basin during most of the Matuyama polarity chron but shoaled rapidly in the early and middle Brunhes in response to a major phase of deltaic progradation. The initial transition to continental sediments occurred during a prominent glacioeustatic low-stand that is likely to be MIS 12 (∼0.43 Ma) but could be as young as MIS 8 (∼0.25 Ma). The Venice area oscillated from below sea level during subsequent major glacioeustatic high-stands to becoming increasingly emergent during major low-stands as the basin continued to fill with marine and continental sediments. Some parts of the Venice area are now emergent for the first time during a glacioeustatic high-stand (i.e., MIS 1 or the Holocene). The total long-term subsidence rate estimated from the VENICE-1 record is less than 0.5 mm/yr, considerably slower than estimates for the Holocene and especially the modern anthropogenic period.Geophysics, Paleoclimate sciencedvk2, gk8Lamont-Doherty Earth ObservatoryArticlesClimate Change in the North Pacific Using Ice-Rafted Detritus as a Climatic Indicatorhttp://academiccommons.columbia.edu/catalog/ac:143416
Kent, Dennis V.; Opdyke, Neil D.; Ewing, Mauricehttp://hdl.handle.net/10022/AC:P:12241Tue, 17 Jan 2012 00:00:00 +0000The variations in weight percent of the grain size fraction greater than 250 Î¼ in nine cores from the North Pacific were determined using sampling intervals of 5 to 20 cm. Material in this size fraction is interpreted as transported by icebergs, and fluctuations are attributed to the waxing and waning of glaciers on the surrounding continents. At least eleven periods of increased ice rafting are detected in the cores during the time from 1.2 m.y. ago to the present, whereas only about four are identified from 1.2 m.y. to 2.5 m.y. B.P. The dating and time correlations are based on the magnetic stratigraphy, ash falls, and faunal extinctions. The ice-rafted detritus indicates a cooling beginning about 1.2 m.y. ago and becoming very intense between the Jaramillo event and the Brunhes-Matuyama boundary. This time may correspond to the initiation of mid-latitude glaciations of Europe and North America. At least six zones of ice-rafted sediment are present in the Brunhes normal polarity series. The correlations between these and the carbonate fluctuations of the central Pacific are good. Evidence for a marked interglacial ranging from about 460,000 to 530,000 yrs B.P. occurs within these cores. This interglacial may be worldwide in extent.Paleoclimate sciencedvk2Lamont-Doherty Earth ObservatoryArticlesIntegrated Paleocene calcareous plankton magnetobiochronology and stable isotope stratigraphy: DSDP Site 384 (NW Atlantic Ocean)http://academiccommons.columbia.edu/catalog/ac:143292
Berggren, William A.; Aubry, Marie-Pierre; Van Fossen, Mickey C.; Kent, Dennis V.; Norris, R. D.; Quillévéré, F.http://hdl.handle.net/10022/AC:P:12207Fri, 13 Jan 2012 00:00:00 +0000At Deep Sea Drilling Site 384 (J-Anomaly Ridge, Grand Banks Continental Rise, NW Atlantic Ocean) Paleocene nannofossil chalks and oozes (∼70 m thick) are unconformably/disconformably underlain (∼168 m; upper Maastrichtian) and overlain (∼98.7 m; upper lower Eocene) by sediments of comparable lithologies. The chalks are more indurated in stratigraphically higher levels of the Paleocene reflecting increasing amounts of biosiliceous (radiolarians and diatoms) components. This site serves as an excellent location for an integrated calcareous and siliceous microfossil zonal stratigraphy and stable isotope stratigraphy. We report the results of a magnetostratigraphic study which, when incorporated with published magnetostratigraphic results, reveals an essentially complete magnetostratigraphic record spanning the interval from Magnetochron C31n (late Maastrichtian) to C25n (partim) (late Paleocene, Thanetian). Integrated magnetobiochronology and stable isotope stratigraphy support the interpretation of, and constrain the estimated duration of, a short hiatus (∼0.9 my) within the younger part of Chron C29r (including the K/P boundary) and an ∼6 my hiatus separating upper Paleocene (Magnetozone C25n) and upper lower Eocene (Magnetozone C22r) sediments. Some 30 planktonic foraminiferal datum levels [including the criteria used to denote the Paleocene planktonic foraminiferal (sub)tropical zonal scheme of Berggren and Miller, Micropaleontology 34 (4) (1988) 362–380 and Berggren et al., SEPM Spec. Publ. 54 (1995) 129–212, Geol. Soc. Am. Bull. 107 (11) (1995) 1272–1287], and nearly two dozen calcareous nannoplankton datum levels have been recognized and calibrated to the magnetochronology. Planktonic foraminiferal Subzones P4a and P4b of (upper Paleocene) Zone P4 are emended/redefined based on the discovery of a longer stratigraphic extension of Acarinina subsphaerica (into at last Magnetozone C25n). Stable isotope stratigraphies from benthic foraminifera and fine fraction (<38 μm) carbonate have been calibrated to the biochronology and magnetostratigraphy. A minimum in benthic foraminifer δ13C was reached near the Danian/Selandian boundary (within Chron C26r, planktonic foraminiferal Zone P3a and calcareous nannoplankton Zone NP4) and is followed by the rise to maximum δ13C values in the late Thanetian (near the base of C25n, in Zone P4c and NP9a, respectively) that can be used for global correlation in the Paleocene.Paleoclimate science, Sedimentary geologydvk2Lamont-Doherty Earth ObservatoryArticlesMilankovitch climate forcing in the tropics of Pangaea during the Late Triassichttp://academiccommons.columbia.edu/catalog/ac:143281
Olsen, Paul E.; Kent, Dennis V.http://hdl.handle.net/10022/AC:P:12205Fri, 13 Jan 2012 00:00:00 +0000During the Late Triassic, the Newark rift basin of Eastern North America was in the interior of tropical (2.5–9.5°N) Pangaea. Strikingly cyclical lacustrine rocks comprise most of the 6770 m of continuous core recovered from this basin by the Newark Basin Coring Project. Six of the seven drill cores (each from 800 to 1300 m long) from this project are used to construct a composite lake-level curve that provides a much needed record of long term variations in continental tropical climate. The correlations on which the composite section is based show complete agreement between lake level cycles and independent magnetic polarity boundary isochrons. The main proxy of lake level and hence climate used to construct this lake level curve is a classification of water-depth related sedimentary structures and fabrics called depth ranks. We then use Fourier frequency analysis (both FFT and multitaper methods) and joint time-frequency approaches to resolve the periodic properties of the cyclicity and the secular drift in those properties. A consistent hierarchy in frequencies of the lake level cycles is present throughout the Late Triassic (and earliest Jurassic) portions of the cores, an interval of about 22 m.y. Calibration of the sediment accumulation rate by a variety of methods shows that these thickness periodicities are consistent with an origin in changes in precipitation governed by celestial mechanics. The full range of precession-related periods of lake level change are present, including the two peaks of the ∼20,000 year cycle of climatic precession, the two peaks of the ∼100,000 year eccentricity cycle, the single peak of the 412,900 year eccentricity cycle, and the ∼2,000,000 year eccentricity cycle. There is also good correspondence in the details of the joint-time frequency properties of lake level cycles and astronomical predictions as well. Even in an ice-free world, the tropical climate of Pangaea responded strongly to astronomical forcing, suggesting that precession-dominated climatic forcing probably always has been a prominent feature of tropical climate.Paleoclimate science, Sedimentary geologypeo1, dvk2Lamont-Doherty Earth Observatory, Earth and Environmental SciencesArticlesA Late Triassic lake system in East Greenland: facies, depositional cycles and palaeoclimatehttp://academiccommons.columbia.edu/catalog/ac:143284
Clemmensen, Lars B.; Kent, Dennis V.; Jenkins, Farish A.http://hdl.handle.net/10022/AC:P:12206Fri, 13 Jan 2012 00:00:00 +0000The Upper Triassic Fleming Fjord Formation of the Jameson Land Basin in East Greenland contains a well-exposed succession, 200–300 m thick, of lake deposits. The Malmros Klint Member, 100–130 m thick, is composed of cyclically bedded intraformational conglomerates, red siltstones and fine-grained sandstones and disrupted dolomitic sediments (paleosols). The cyclicity is composite with cycles having mean thicknesses of (25), 5.9 and 1.6 m. The overlying Carlsberg Fjord beds of the Ørsted Dal Member, 80–115 m thick, are composed of structureless red mudstones rhythmically broken by thin greyish siltstones. This unit also has a composite cyclicity with cycles having mean thicknesses of 5.0 and 1.0 m. The uppermost Tait Bjerg Beds of the Ørsted Dal Member, 50–65 m thick, can be divided into two units. A lower unit is composed of cyclically bedded intraformational conglomerates or thin sandstones, red mudstones, greenish mudstones and yellowish marlstones. An upper unit is composed of relatively simple cycles of grey mudstones and yellowish marlstones. Recognized cycles have mean thicknesses of 5.6 and 1.6 m. The lake deposits contain evidence of seasonal, orbital and long-term climatic change. Seasonal change is documented by numerous desiccation surfaces especially in the Malmros Klint Member and Carlsberg Fjord beds, orbital change is suggested by the composite cyclicity, and long-term climatic change is indicated by the systematic upwards change in sedimentary characteristics of the lake deposits. The sedimentary features of the Malmros Klint Member suggest lacustrine deposition in a dry climate that fluctuated between desert and steppe conditions, the Carlsberg Fjord beds probably record lacustrine lake deposition in a rather constant dry (steppe) climate, while the Tait Bjerg Beds record lake sedimentation in a climate that fluctuated between dry (steppe) and warm moist temperate. In the Tait Bjerg Beds the upward change in cycle characteristics indicates a shift towards more humid conditions. Climatic deductions from sedimentary facies are in good agreement with climate maps of Laurasia, as simulated by numerical climate models. Palaeomagnetic data indicate a northward drift of East Greenland of about 10° from ca. 25°N to ca. 35°N in the Middle to Late Triassic. The Fleming Fjord Formation which represents ca. 5 m.y. of the Late Triassic interval was deposited during latitudinal drift of 1–2°. It is possible that the observed long-term upward shift in climatic indicators within the formation can be ascribed to plate drift, but southward shift of climatic belts could also have been of importance.Paleoclimate science, Sedimentary geologydvk2Lamont-Doherty Earth ObservatoryArticlesThe Early Carboniferous paleomagnetic field of North America and its bearing on tectonics of the Northern Appalachianshttp://academiccommons.columbia.edu/catalog/ac:142199
Kent, Dennis V.; Opdyke, Neil D.http://hdl.handle.net/10022/AC:P:11895Mon, 05 Dec 2011 00:00:00 +0000We have obtained additional evidence for the Early Carboniferous paleomagnetic field for cratonic North America from study of the Barnett Formation of central Texas. A characteristic magnetization of this unit was isolated after thermal demagnetization at four sites (36 samples) out of eight sites (65 samples) collected. The mean direction of declination = 156.3°, inclination = 5.8° (N = 4 ,k = 905 , α95 = 3.0°), corresponds to a paleomagnetic pole position at lat. = 49.1°N,long. = 119.3°E (dp = 1.5° , dm = 3.0°). Field evidence suggests that characteristic magnetization was acquired very early in the history of the rock unit whereas the rejected sites are comprised of weakly magnetized limestones dominated by secondary components near the present-day field direction. Comparison of the Barnett pole with other Early Carboniferous (Mississippian) paleopoles from North America shows that it lies close to the apparent polar wander path for stable North America and that the divergence of paleopoles from the Northern Appalachians noted previously for the Devonian persisted into the Early Carboniferous. We interpret this difference in paleopoles as further evidence for the Northern Appalachian displaced terrain which we refer to here as Acadia, and the apparent coherence of Late Carboniferous paleopoles as indicating a large (∼1500 km) motion of Acadia with respect to stable North America over a rather short time interval in the CarboniferousPaleoclimate science, Plate tectonicsdvk2Lamont-Doherty Earth ObservatoryArticlesOrigin of Magnetic Instability in Sediment Cores From the Central North Pacifichttp://academiccommons.columbia.edu/catalog/ac:137869
Kent, Dennis V.; Lowrie, Williamhttp://hdl.handle.net/10022/AC:P:11020Mon, 29 Aug 2011 00:00:00 +0000Previous paleomagnetic studies on deep-sea sediment cores from the central North Pacific have shown that the natural remanent magnetization (NRM) of these 'red clay' sediments was unstable below several meters depth in each core. It was also noted that the magnetic instability was related to the presence of a relatively large low-coercivity component of magnetization. The purpose of this investigation was to characterize the rock magnetic properties in three select cores from this region to determine the physical origin of the unstable magnetization. The principal findings of our investigation were as follows. (1) The ability to acquire a viscous remanent magnetization increased with depth in each core, particularly at about the level where unstable magnetization became evident. (2) The magnitude and stability of the observed NRM of the magnetically unstable section of each core can be explained by a viscous remanence acquired in the presence of the earth's magnetic field over a period of time ranging from only several weeks to several thousands of years. (3) The unstable magnetization, believed to be of viscous origin, was attributed to the presence of a magnetic mineral similar in structure and composition to maghemite. This mineral may have resulted from the low-temperature oxidation of very fine grained magnetite at about the time of deposition of these sediments. The extrapolated ages of the levels at which unstable magnetization becomes evident in the cores from this region suggest a close correspondence with the times of established upper Cenozoic climatic changes. Considerations of the alteration of the sedimentary regime resulting from the changes in climate can provide a satisfactory explanation for the observed change in magnetic properties.Geophysics, Paleoclimate sciencedvk2Lamont-Doherty Earth ObservatoryArticles